1. Field of the Invention
This invention relates generally to an electromagnet controlled scanning shutter blade system, and more particularly, to a photographic scanning shutter blade arrangement wherein the closing movement is controlled by way of an electromagnet actuated drive which may be recocked in a simple manner.
2. Description of the Prior Art
Thin and compact photographic cameras of the reflex type have been developed wherein the exposure of the film unit is electronically controlled and the film unit may be rapidly processed at a processing station within the photographic camera. A version of such a camera having a compactness and thinness suited to permit convenient carrying in the pocket of a garment is described in U.S. Pat. No. 3,672,281, entitled "Reflex Camera" by E. H. Land. Such cameras are of the single lens reflex variety and require a complex exposure control system in order to accommodate a requisite viewing and focusing mode during which time the single lens reflex camera is in a normally open status to unblock the passage of light through the exposure opening to a viewfinder. An exposure control system ideally suited for such a camera is described in U.S. Pat. No. 3,641,889, issued by V. K. Eloranta. This exposure system is characterized by the use of a tractive electromagnetic device, preferably a solenoid, for controlling the movement of a pair of "scanning type" shutter blade elements. Use of a solenoid driven "scanning type" shutter system allows for the development of dual exposure parameter regulation (aperture and speed) of the exposure value of any given exposure. For instance, following an initial energization of the solenoid, it may be deenergized to permit the blades of the exposure mechanism to progressively open under a spring bias to define a gradually enlarging aperture. The exposure interval may then be terminated by again energizing the solenoid to rapidly drive the exposure mechanism blades to a closed orientation. Controlled initial deenergization of the solenoid for purposes of commencing exposure interval, as well as subsequent energization of the solenoid to terminate an exposure interval, is carried out by an electronic control circuit which operates in conjunction with a light sensing network arranged to be responsive to light levels of the scene being photographed. Such solenoid actuated "scanning type" shutter blade arrangements have also been utilized in non-reflex cameras such as Polaroid Corporation's newly marketed Pronto type cameras.
The use of a solenoid to drive a "scanning type" shutter blade arrangement is limited, however, in the speed at which the shutter blade elements can be driven from their scene light blocking position. Solenoids include an internally disposed plunger or armature which is drawn within an excitation winding during the energization thereof and the acceleration of the plunger is limited by the time delay required for the solenoid to develop a maximum magnetic flux condition to arrest the outward movement of the plunger from the excitation winding. Solenoid actuated shutter blades may also encounter pull and time variations due to power variations in the camera power supply.
One attempt at solving the problems encountered as a result of voltage level variations in a camera battery supply which might affect the solenoid pull in time is disclosed in U.S. Pat. No. 3,922,698 entitled "Dynamically Compensated Exposure Control System" by C. Peterson, issued Nov. 25, 1975. Peterson discloses an exposure control system wherein the actuating drive or solenoid of the system is coupled to be operated only against a substantially constant force of a spring bias, while the exposure mechanism movement with its attendant mass acceleration characteristics is provided by a spring drive isolated from the spring bias against which the solenoid is driven. Thus, by isolating the solenoid from the spring drive serving to close the shutter, there may be provided a constant rate of shutter blade closing despite variations in the power supply to the camera. However, the shutter blade closing speed is still limited by the time required to pull in the solenoid plunger as is the case where the solenoid operates directly on the shutter blade mechanism to drive the shutter blades to their scene light blocking position.
Shutter blade arrangements embodying two electromagnets as disclosed in U.S. Pat. No. 3,593,630 entitled "Breaking and Sequencing Mechanism" by L. Douglas et al., issued July 20, 1971, can provide quicker shutter blade closing times than are possible with the aforementioned solenoid actuated "scanning type" shutter arrangement. The Douglas shutter arrangement, however, is not of the "scanning type" and thus does not provide the advantages appertaining to a "scanning type" shutter blade arrangement, i.e., greater depth of field resulting from a slow progressive opening of the aperture. The aperture of Douglas is defined instead by a diaphragm element separate and distinct from the shutter closing assembly which is controlled by the electromagnets.
Therefore, it is a primary object of this invention to provide a camera exposure control system embodying "scanning type" shutter blade elements which may be quickly closed without the use of a solenoid.
It is a further object of this invention to provide a camera exposure control system for use with "scanning type" shutter blade elements wherein the exposure may be quickly terminated by way of a shutter blade closing drive spring actuated through an electromagnet.
Other objects of the invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.